The invention concerns a device and a method for the testing of decoking tools.
As is well known, decoking tools are used in refineries in context with the emptying of coke drums, in which refineries coke remains at the end of processing crude oil, the coke being collected in coke drums of e.g. 30 m of height and a diameter of 8 m. Once the coke drums are full they are emptied within the shortest possible period of time so that they will be available again as soon as possible for receiving newly accruing coke.
For the emptying of coke drums, so called decoking tools are employed which are provided with boring nozzles and cutting nozzles. Such a tool is mounted on the lower end of a hollow drill stem which is guided on a frame above the boring drum so as to be lifted and lowered and which is supplied with pressurized water via high-performance pumps. On emptying the coke drums the decoking tool is guided through the coke drum, initially starting at the top and moving towards the bottom for boring-up a central vertical channel by means of the now rotating drill stem, wherein water jets exit from the boring nozzles arranged on the underface of the decoking tool at high-pressure, crushing the coke and pushing it away so that the required central bore can be formed in the coke drum. Having arrived at the bottom, the decoking tool is switched from boring to cutting, so that the water jets are no longer discharged from the boring nozzles but from two cutting nozzles diametrically opposing each other on the circumference of the decoking tool. The decoking tool is now lifted, again whilst rotating, by the drill stem. Herein, the water jets exiting from the cutting nozzles break the coke over the whole cross-section of the drum up to the drum wall, so that the coke may fall downwardly in the drum and may be delivered from an opening at the lower end of the drum.
The cutting performance of the decoking tools depends on parameters such as the pressure of the water in the nozzles (e.g. approximately 350 bar), the diameter of the nozzles, the type and temperature (e.g. 300-700° C.) of the coke and other factors.
In the development of decoking tools up to date, testing of function can only be carried out on components or component assemblies of the tools such as valve controls, flow channels etc. and this is done under testing conditions with conditions and demands reduced in relation to practice. In the development of novel nozzle geometries for improving the cutting performance one is also restricted to model calculation and to tests which are supported by assumptions concerning the profile of the pressurized water jet in practice. It is rather unsatisfactory when the development results may only be tested theoretically or by means of testing equipment not allowing safe conclusions regarding the factual function during operation in practice. As a result, enhancements such as the geometry of cutting nozzles and boring nozzles, whose effects on the cutting performance very essentially depend on the water pressure present immediately within the nozzle, can only be judged reliably in practical operation in the coke drum. Even there, the options for distinguished perceptions are limited because the function of the decoking tool can only be tested very roughly due to the conditions within the coke drum.